Final answer:
GERD is the reflux of gastric contents into the lower esophagus due to decreased functioning of the lower esophageal sphincter (LES). It can lead to heartburn and potentially gastroesophageal reflux disease (GERD).
Step-by-step explanation:
Gastroesophageal reflux disease (GERD) is the reflux of gastric contents into the lower esophagus due to decreased functioning of the lower esophageal sphincter (LES). The LES normally remains closed to prevent the contents of the stomach from entering the esophagus. However, when the LES fails to remain completely closed, it can lead to heartburn. If this occurs chronically, it can result in GERD, where the mucous membrane of the esophagus may become damaged by the highly acidic contents of the stomach.